Creating and Editing a Hierarchical Schematic
Hierarchy is an essential part of chip design. In this tutorial we will learn how to create
and work with a hierarchical schematic.
It is assume that that you have already created a schematic of a NOR2 and a symbol.
Below is the schematic that we will be creating:
First we need to create a new cell. In this we will place the 3 NOR symbols
1) From the toolbar at the top of the Library Manager select: Files->New-> Cell
View
2) You will see the create new file pop-up
menu shown below
3) Under Library Name select the library where
you want your new cell to be (here we have
selected bolson_class)
4) Under Cell Name enter the name of you new
cell (here we have “three_nors”) – do not
have spaces in the name or weird characters
5) Select Composer-Schematic as the Tool
6) The View Name will be changed to
schematic
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7) You will see an empty schematic composer window.
We will now place ONE nor2 – The nor2 that you previously created
8) Hit bindkey i – to instantiate an instance
9) You will se the pop-up menu below
10) Select Browse
11) You will see something that looks like a Library Manger window. (see below)
12) Select the nor2 cell that you previously created. Be sure to select Symbol View.
13) Hit Close to close the window
14) The Add instance window will now be properly filled out.
15) Hit Hide to close
In the schematic Composer Window
16) Place one nor2
17) Hit <esc> to end the command
18) Connect four wires to the nor2 gate and name one vdd and two gnd (see below)
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We will now copy this two more times, so that we have three nor2 gates
19) Draw a selection box around the nor gate and the wires (see below)
20) Hit bindkey c (copy)
21) With your left mouse button click to define an origin
22) Move your cursor to the destination
23) With your left mouse button click on the destination
24) Repeat steps 20-23 to place the third inverter
Below is a completed schematic
Note all the powers (vdd) and grounds(gnd) are connected
Left mouse click
to define an origin
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Left mouse click to
define destination
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Name the unnamed wires:
25) In the schematic window on the toolbar on the left
hand side. Hit the add wire name icon
Name the wires: in, out1, out2, out3
Below is the scematic with all the nets named
Add pins for: in, out3 vdd and gnd
26) Hit bindkey p (add pin)
27) Type in the names for the pins separated by spaces.
Recommendation:
in (Direction input)
out (Direction output)
vdd (Direction InputOutput)
gnd (Direction InputOutput)
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28) Below is the resulting schematic. Note the pins have the same names as the
wires and are assumed to be connected
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Frequently it is helpful to “descend in the hierarchy”
29) Select one of the nors on your schematic
30) From the top toolbar in the schematic composer window select:
Design->Hierarchy->Descend Edit -- bindkey X (shift-x)
31) When prompted hit <OK>
32) You will now be in the schematic for the nor2 (see below). You can tell this by
looking at the top of the window
Check and
save
33) In this window you an edit the schematic for nor
34) When you are done making changes hit the Check and save icon
35) To return to your original schematic:
Bindkey b go up one level of hierarchy
Bindkey B go to the very top of the hierarchy
or from the top toolbar select: Design->Hierarchy->return
36) Back in your original schematic composer window
37) check and save your work
38) Close the window
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